Conducting polymers

ABSTRACT

An electrically conducting composition is described which comprises a polyarylene, e.g. polyphenylene, and a suitable doping agent, e.g. ferric chloride. The polyarylene is prepared from a poly(1,2-disubstitutedcyclohexa-3,5-diene).

This is a division of application Ser. No. 597,389 filed Apr. 6, 1984,now U.S. Pat. No. 4,548,737 issued 10-22-86.

This invention relates to the use of polyarylenes in electrical andelectronic applications.

Electrically conducting compositions derived from polyphenylene areknown.

We have now devised electrically conducting compositions which comprisecertain polyarylenes described in our copending European patentapplication No. 82305028.1, the disclosure of which is incorporatedherein by way of reference, and suitable doping agents.

By "electrically conducting composition" we mean a composition which hasa direct current conductively of at least 10⁻⁵ ohm⁻¹ cm⁻¹ when measuredby the four-probe method at room temperature.

By "four-probe method" we mean the known and accepted art method ofmeasuring the electrical conductivity of a polymeric film or materialusing either A.C. or D.C. current between four contacts as described in,for example, Journal of the American Chemical Society 1978, 100, pages1014-1016.

According to a first aspect of the present invention there is providedan electrically conducting composition comprising a polyarylene preparedfrom a poly(1,2-disubstituted-cyclohexa-3,5-diene) and a suitable dopingagent.

According to a second aspect of the present invention there is provideda process for the preparation of an electrically conducting compositionwhich process comprises (A) the steps of doping apoly(1,2-disubstitutedcyclohexa-3,5-diene) with a suitable doping agentand then converting the polycyclohexadiene into a polyarylene or,preferably (B) the steps of converting apoly(1,2-disubstitutedcyclohexa-3,5-diene) into a polyarylene and thendoping the polyarylene with a suitable doping agent.

Arylene homo- or co-polymers of which electrically conductingcompositions according to the first aspect of the present invention arecomprised preferably have structures represented by the general formula##STR1## wherein the residues Ar and X, where X is present, may varyfrom unit to unit in the polymer chain, Ar represents a divalentaromatic or substituted aromatic group, X is a residue of one or morepolymerisable comonomers as hereinafter defined, n and m are wholenumbers and the ratio of n:m lies in the range 1:0 to 1:100.

The 1,2-disubstituted-cyclohexa-3,5-diene homo- or co-polymer used inthe process according to the second aspect of the present inventionpreferably has a structure represented by the general formula ##STR2##wherein the cyclohexenylene ring and the residue X, where X is present,may vary from unit to unit along the polymer chain; each R', which maybe the same or different, is hydrogen, hydrocarbyl, e.g. lower alkylhaving up to five carbon atoms, aroyl, alkanoyl having up to ten carbonatoms, or preferably R² OCO, where R² is aryl or an alkyl group havingup to ten carbon atoms, preferably one or two carbon atoms; X, n and mhave the meanings hereinbefore ascribed to them.

By "polymerisable comonomer" we mean a compound which can be reactedunder polymerisation conditions with a1,2-disubstituted-cyclohexa-3,5-diene which has 1,2-substituents asherein defined to form a copolymer therewith.

Examples of suitable polymerisable comonomers the residues of which maybe present in copolymers of general formula I or II include inter aliavinyl monomers, for example, olefinic hydrocarbons, e.g. styrene,methacrylates, vinyl halides, vinyl esters, acrylonitrile andtetrafluoroethylene; and compounds such as sulphur dioxide.

In polymers of general formula I, Ar is preferably a phenylene ring. Thelinkages by which the phenylene rings are bonded in the polymerbackbones may be ortho or para to each other, and it is often preferredthat a majority of the linkages are para.

In polymers of general formula II, the polymer backbone preferablycomprises both cyclic ring ##STR3## and cyclic ring. ##STR4##

The 1,2-substituents in the poly(1,2-di-substituted-cyclohexa-3,5-diene)which are used in the process of the second aspect of the presentinvention are conveniently cis to each other since such polymers may bederived from cis-1,2-dihydroxycyclo-hexa-3,5-dienes which may be readilyprepared by bio-chemical processes as is more fully described in ourEuropean patent application Publication No. 76606A. However, we do notexclude the possibility that the aforesaid substituents may be trans toeach other, since such systems may be readily converted intopolyarylenes as shown in our European patent application No. 82305028.1.

As additional, non-preferred, examples of the aforesaid 1,2-substituentsmay be mentioned inter alia amide, halide, thioester, urethane andxanthate.

By "suitable doping agent" we mean electron donor or acceptor materials,or mixtures thereof, which are known to be useful in increasing theconductivity of organic materials.

As examples of suitable doping agents of which electrically conductingcompositions according to the present invention may be comprised may bementioned inter alia electron donor agents such as Group IA metals, e.g.lithium, sodium, potassium and Group IA metal arenes, e.g. sodium andpotassium naphthalene and sodium and potassium biphenyl; and electronacceptor agents such as Bronsted acids, e.g. HClO₄ ; non-metal oxides,e.g. SO₃ and N₂ O₅, Group VB sulphides, e.g. Sb₂ S₅, halides of GroupsVB, VIA, IB, IIIB, IVB and the inert gases, e.g. SbCl₅, SbF₃ Cl₂, AsF₅,PF₅, CrO₂ Cl₂, CrO₂ F₂, FeCl₃, MoCl₅, CuCl₂, BCl₃, SnCl₄, and XeF₄.

All references to the Periodic Table are to the Periodic Table ofElements in "Advanced Inorganic Chemistry" Third Edition, 1972, byCotton and Wilkinson, Interscience.

The type of doping agent chosen depends upon the electroniccharacteristics desired in the electrically conducting composition ofthe present invention. Electron donor materials provide an n-typeelectrically conducting composition of the present invention. Electronacceptor materials provide a p-type electrically conducting composition(hole conductivity).

The interface between electron donor-doped and acceptor-dopedcompositions provides an n-p junction which can serve, for example, as arectifier.

The concentration of doping agent in the electrically conductingcompositions of the present invention is from about 10⁻⁵ to 0.5 mole permole of arylene unit in the polyarylene, and preferably 10⁻³ to 0.1.

The poly(1,2-disubstituted-cyclohexa-3,5-dienes) used in the process ofthe present invention may be prepared as described in our aforesaidEuropean patent application No. 82305028.1.

The conversion of a poly(1,2-disubstituted-cyclohexa-3,5-diene), eitherdoped or undoped, into a polyarylene in the process according to thepresent invention may be carried out as described in our aforesaidEuropean patent application No. 82305028.1 or preferably in the presenceof an organic amine, particularly preferably an alkylamine in which thealkyl group has up to ten carbon atoms, more particularly preferably atertiary alkylamine, e.g. tri-n-octylamine, as described in our Europeanpatent application No. 83305174.1, the disclosure in which isincorporated herein by way of reference.

In the process according to the present invention procedure B ispreferred since the products thereof have higher electricalconductivities than the product of procedure A.

In the process according to the present invention the doping step may becarried out by any of the processes known in the electronics art fordoping polymers with suitable dopants. As examples of such processes maybe mentioned inter alia addition of the doping agent from the gas phase,mixing of doping agent and polyarylenes in the solid or melt phase, orpreferably deposition of the doping agent from solution orelectrochemically.

Where, in the process according to the present invention, thepolyarylene is treated with a solution of a suitable doping agent thesolvent therefor is preferably a polar aprotic solvent (a) in which thedoping agent can be dissolved to form a concentrated solution and (b) towhich the polyarylene is substantially inert, e.g. it is essentiallyinsoluble therein. As examples of suitable solvents may be mentionedinter alia dioxan, diglyme, N,N-dimethylformamide and preferablynitromethane. The concentration of the aforesaid solution is typicallybetween 5% w/w and 10% w/w.

Where, in the process according to the present invention, thepolyarylene is treated with a solution of suitable doping agenttreatment is typically carried out for between a few minutes and tens ofhours, and conveniently is carried out at ambient temperature.

The polymers used in the process according to the present invention andelectrically conducting compositions according to the present inventionmay be in a variety of forms. For example, they may be particulate,fibrous, in the form of a three-dimensional solid or preferably in theform of a substantially continuous two-dimensional solid, e.g. a film orcoating.

Where the electrically conducting composition according to the presentinvention is a substantially continuous two-dimensional solid it may bein the form of a self-supporting layer, e.g. a film, typically having athickness between 10 and 200 microns, or a coating or encapsulatinglayer, typically having a thickness of up to a few microns, on asuitable substrate, e.g. glass or a metal.

By the process of the present invention, particularly procedure B,continuous films and coatings of electrically conducting compositionscomprising a polyarylene and a suitable dopant which have a greatersurface area than hitherto known films and coatings of electricallyconducting polyphenylene compositions can often be prepared.

The present invention is further illustrated with reference to thefollowing examples.

EXAMPLES 1-3

A solution of poly(cis-1,2-dipivaloxycyclohexa-3,5-diene) (7.5 grams),prepared as described in Example 34 of European patent Publication No.76605, in squalane (500 ml) was heated under nitrogen at reflux for 6hours. An increasing quantity of a pale yellow precipitate was producedover the duration of the experiment. The mixture was cooled, filtered,washed with pentane and dried to leave polyphenylene powder.

Samples (200 mgs) of the polyphenylene powder were treated with clearportions (15 mls) of a solution, obtained by dissolving ferric chloride(5 grams) in nitromethane (80 mls) and allowing the mixture to standovernight, in a nitrogen atmosphere for defined periods of time; withina couple of minutes the polyphenylene turned black. The products werefiltered off, washed with nitromethane, dried under vacumm, and theirchemical compositions determined.

The products were separately pressed into discs (15 mm diameter, 1 mmthick) and the electrical conductivity thereof was measured using aconventional 4-point probe technique. The results are given in Table 1.

                  TABLE 1                                                         ______________________________________                                        Example                                                                              Reaction Conductivity Empirical                                        No     Time     (ohm.sup.-1 cm.sup.-1)                                                                     Formula                                          ______________________________________                                        1       2 mins  0.12 × 10.sup.-2                                                                     [C.sub.6 H.sub.4.46 (FeCl.sub.4.05)0.070].sub                                 .x                                               2       3 hrs   1.1 × 10.sup.-2                                                                      [C.sub.6 H.sub.4.7 (FeCl.sub.4.1)0.078].sub.x                                 1                                                3      20 hrs   1.5 × 10.sup.-2                                                                      [C.sub.6 H.sub.4.2 (FeCl.sub.4)0.102].sub.x      ______________________________________                                    

EXAMPLE 4

A solution of poly(bis-methylcarbonate ofcis-1,2-dihydroxycyclohexa-3,5-diene) (5 grams), and tri-n-octylamine(300 microliters) in 1,4-dioxan (30 mls) was spin coated onto a glassmicroscope slide at 3000 rpm to give a colourless coating.

The coated slide was placed in an oven in a nitrogen atmosphere and thetemperature was raised continuously over 1 hour to 410° C. to produce acoating, 1.2 microns thick, of polyphenylene.

The microscope slide coated with polyphenylene was immersed in theferric chloride solution described in Example 1 for 3 hours, it was thenwashed with quantities of nitromethane until no yellow colour wasextracted from the coating. The slide was dried and the conductivity ofthe coating was found to be 10⁻³ to 10⁻⁴ ohm⁻¹ cm⁻¹ (determined using afour terminal procedure in a nitrogen atmosphere.) In the four terminalprocedure, one Keithly 610 electrometer was used to measure voltage anda second Keithly 610 electrometer was used to measure current; theelectrodes comprised four parallel silver wires attached to the coatingwith silver paint.

EXAMPLE 5

This Example describes the preparation of an electrically conductingpolyphenylene composition by an electrochemical process in a nitrogenatmosphere.

In an electrochemical cell, the working electrode was a substantiallycolourless film of polyphenylene on a platinum coated glass slidemeasuring 1 cm×2 cm (prepared as described in Example 4); the counterelectrode was a thin platinum coil; the reference electrode was a silverwire; and the electrolyte was a 0.1 molar solution of lithiumhexafluoroarsenate in propylene carbonate (distilled, dried over amolecular sieve and deoxygenated).

Current-potential curves indicated two anodic peaks, the first at +1.5 vand the second at +2.0 v versus the silver electrode, indicating thepresence of oxidised polyphenylene with hexafluorarsenate anion actingas counterion. The colour of the polyphenylene film became dark brown toblack.

We claim:
 1. A process for the preparation of an electrically conductingcomposition which process comprises:(A) the steps of doping apoly(1,2-disubstitutedcyclohexa-3,5-diene) with a suitable doping agentand then converting the said polycyclohexadiene into a polyarylene; or(B) the steps of converting apoly(1,2-disubstituted-cyclohexa-3,5-diene) into a polyarylene and thendoping the polyarylene with a suitable doping agent wherein (C) the saidpolycyclohexadiene has the structure ##STR5## wherein thecyclohexenylene ring and X, where X is present, may vary from unit tounit in the polymer chain,each Y, which may be the same or different, isamide, halide, thioester, urethane, xanthate or OR' where each R' ishydrogen, hydrocarbyl, aroyl, alkanoyl or R² OCO where R² is aryl or analkyl group having up to 10 carbon atoms, X is a residue of one or morepolymerisable comonomers selected from the group consisting of styrene,methacrylates, vinyl halides, vinyl esters, acrylonitrile,tetrafluoroethylene and sulphur dioxide, n and m are whole numbers andthe ratio of n:m lies in the range 1:0 to 1:100; (D) the said suitabledoping agent is selected from the group consisting of Group IA metals,Group IA metal arenes, Bronsted acids, non-metal oxides, Group VBsulphides and halides of Groups VB, VIA, IB, IIB, IVB and the inertgases; (E) wherein the concentration of doping agent in the electricallyconducting composition is from about 10⁻⁵ to 0.5 mole per mole ofarylene unit in the polyarylene.
 2. A method as claimed in claim 1wherein the poly(1,2-disubstitutedcyclohexa-3,5-diene) has the structure##STR6## wherein the cyclohexenylene ring and X, where X is present, mayvary from unit to unit in the polymer chain,each R¹, which may be thesame or different is hydrogen, hydrocarbyl, aroyl, alkanoyl, or R² OCO,where R² is aryl or an alkyl group having up to 10 carbon atoms, and X,n and m have the meanings ascribed to them in claim
 1. 3. A method asclaimed in claim 1 wherein the conversion step is catalysed by atertiary alkylamine.
 4. A method as claimed in claim 1 wherein thedoping step is carried out by treating thepoly(1,2-disubstitutedcyclohexa-1,3-diene) in procedure A or thepolyarylene in procedure B with a solution of the doping agent.
 5. Amethod as claimed in claim 1 whereing thepoly(1,2-disubstitutedcyclohexa-3,5-diene) used in procedure A or thepolyarylene used in procedure B is in the form of a substantiallycontinuous two dimensional solid.